Emergency lighting unit



Dec. 1, 1964 E. T. DUNCAN 3,159,755

EMERGENCY LIGHTING UNIT Filed Sept. 10, 1962 2 Sheets-Sheet 1 Dec. 1, 1964 E. T. DUNCAN EMERGENCY LIGHTING UNIT 2 Sheets-Sheet 2 Filed Sept 10, 1962 INVENTOR flTTOR/VEYS United States Patent Office 3,159,755 @it Llhglill'lllhlt UNTT Edward T. Duncan, Westport, (Donn, assignor to The Maintenance (Iompany, incorporated, Long island @ity, Nfifi, a corporation of New York Filed Sept. lid, 1%2, No. 222,574 9 (Qt. 3tl7-3$.5)

This invention relates to an emergency lighting unit and, more particularly, to such a unit which has a long life and operates in response to ambient light conditions.

It is very common to install emergency lighting units in areas where public lighting is required. For example, the hallways of most public buildings, such as schools and oflice buildings, are often equipped with emergency lighting units spaced at various intervals along the corridors. These units become actuated upon a power failure and normally supply light from a self-contained battery source. Similarly, elevators are often supplied with such units to prevent panic and accident in the event of stalled elevators and loss of power.

The lighting units customarily employed in the past have most often been actuated by loss of power. While this type unit may be satisfactory for those areas where a number of lighting units are present, they are completely unsatisfactory in areas which are limited in size, such as elevator cabs. This is so because light failure may often occur without power failure. For example, light bulbs may burn out. If this should occur in a long hallway Where a number of other lights are present, there would be no problem, and the fact that an emergency lighting unit failed to come on would not affect the general lighting level. However, the situation would be entirely different if a light burnout occurred in an elevator cab. In an instance such as this, for example, a cab may be stalled between floors. If an electric light should burn out while power is still in the cab, the effect on the occupants may be imagined. Prior art emergency units would not be actuated under such circumstances and the cab would remain dark.

Another feature of prior art emergency lighting units is that they are normally controlled by relays which receive their power from the building power circuit. Many additional problems are raised by the use of relays which it would be desirable to overcome. For example, relays are normally energized at all times. This means that the relay coil is continually consuming power and, therefore, generating heat. This causes the life of the relay to be shortened and the unit to become inoperative after a relatively short period of time. Furthermore, the fact that the relay is consuming power is an additional expense, which it would be desirable to overcome. Finally, the use of relays means that moving mechanical parts are being relied upon to accomplish the switching function. Mechanical parts are subject to wear and sticking, and are sensitive to vibration.

It is, therefore, the object of the invention to provide an improved emergency lighting unit which is not subject to the deficiencies of the aforementioned prior art apparatus. 7

Other objects are to provide such a unit which utilizes no moving parts, which does not consume significant power continuously, which is initiated by lack of light rather than by lack of power, which is insensitive to vibrations, which is not subject to filament burnout, which is substantially fail-safe in that the device remains in a static condition during operation, and which is substantiflly maintenance-free.

The manner in which the foregoing objects are attained will be more apparent from the following description, the appended claims and the figures of the attached drawings, wherein FIG. 1 is a circuit diagram of an emergency lighting unit in accordance with this invention;

PEG. 2 is a circuit diagram of a variation of the emergency lighting unit shown in FIG. 1, and

FIG. 3 is a pictorial view of an actual emergency lighting unit constructed in accordance with this invention with the cover removed.

The objects of this invention are achieved by means of a novel voltage divider circuit. The voltage division ratio of this circuit varies in accordance with the ambient light level. The voltage existing at a given point on the divider circuit actuates a gate which controls the flow of current through a lamp. During normal operation, a supply battery is maintained in a continuous state of energization by means of a trickle charge.

A more detailed description of this invention will now be given with particular reference to the circuit of FIG. 1. A power transformer iii has a primary winding 12 that is energized from a power source 14. The secondary winding 18 of transformer id is provided with a mid-tap 2t? and end connections 22, 24. The positive pole of a nickel-cadmium rechargeable battery 26 is connected to terminal 22 of secondary transformer winding 18. Terminal 24 of winding 18 is connected to a series circuit including resistor 2S and a diode 3d. Diode 30 is also connected to the negative side of battery 26 so that a complete circuit is formed. In order to simplify the circuit description, the electrical connection between diode 30 and the negative terminal of battery as will be referred to as negative bus 32. A switch 34 and a lamp 3d are in series with a parallel circuit comprising capacitor 38 and silicon-controlled rectifier as between mid-tap 2t of transformer secondary l8 and negative bus 32. Across the terminals of battery 26 there is provided a voltage divider circuit comprising a fixed resistor 42 and a cadmium sulfide photosensitive resistor 44. From a mid-tap 46 between resistor 42 and photosensitive resistor 44, a diode 48 is connected so as to conduct current toward the gate of the silicon-controlled rectifier 49. A capacitor 50 and a 40,000 ohm resistor 52 are connected in parallel between negative bus 32 and the gate of the silicon-controlled rectifier 40.

Switch 34 functions as a shut-off switch for the entire unit. For elevator use, for example, this switch would be opened when the elevators are shut down at the end of a day. Even when switch 3 is open, however, the trickle charge on battery 26 is maintained.

In order to facilitate the understanding of the operation of this circuit, the following descriptions are given to illustrate its function in three different situations.

Power and Light On This would be the normal operation of this invention. it will be understood that the unit, in all probability, will be a self-contained unit and that the cadmium-sulfide photosensitive resistor 44 will be mounted so as to be exposed to ambient light levels. Under the assumed conditions, power is present at the primary winding 12 of transformer it and the ambient lighting level in the area is normal. lit will be noted that a complete circuit is formed by the secondary winding ll of transformer lo, the nickel-cadmium battery 26, the negative bus 32, the diode 3d, and the resistor 23. Diode 3d is a half-wave rectifier. Therefore, current will only flow in this circuit during each half cycle. However, during this half cycle, a small trickle charge current passes from the transformer to the battery 26, maintaining the battery in a constant state of charge.

At the same time, a cadmium-sulfide photosensitive resistor is being exposed to a light level sufllciently intense to maintain its resistance at a low value. The low resistance value of resistor serves to effectively position tap 46 near the negative pole of the nickel-cadmium storage battery as. Thus, the voltage existing at this point is very close to the voltage existing on bus 32., and, consequently, the diode 48 will be unable to conduct current. If no current is conducted to the gate of siliconcontrolled rectifier dil, this rectifier acts as a switch and prevents passage of current through lamp 36.

in summary, when both main power and general lighting in the area are on, the emergency lighting unit of this invention remains off. However, the storage batteries included in the unit are maintained in a perpetual state of charge. Furthermore, it is important to note that no relays and no electronic tubes are employed. Therefore, there is negligible power consumption and there can be no failure because of mechanical breakdown, vibration, or filament burnout.

Power On--Lights Ofi Under these conditions, the transformer it? will be receiving power from power source 14. However, the cadmium-sulfide photosensitive resistor 44- will not be receiving ambient light. Accordingly, the resistance of resistor 54 will increase. As resistors 42 and 4-4 form a voltage divider circuit, the change in resistance ratio has the effect of moving tap 46 toward the positive pole of battery 26. This increases the potential difference between diode 48 and bus 32 until the level is reached at which the diode begins to conduct current. The conduction of current through diode 48 to gate of siliconcontrolled rectifier 4t actuates the rectifier and allows the passage of current from anode to cathode. With conduction through the silicon-controlled rectifier it a new circuit is formed. Current now passes directly from midtap through switch 34, lamp 36, and rectifier to negative bus 32. It will be apparent that a light failure with retention of the power supply will cause the emergency light unit to come on.

Under these conditions it may be assumed that a power failure has taken place. Not only has the ambient light level dropped to a low value, but there is no power prescut to energize transformer it Under these conditions, therefore, there will be no AC. component present in the circuit. As light no longer reaches the photosensitive resistor 44, its resistance increases rapidly. The voltage across this resistor increases and tap 46 becomes more positive. When this occurs, diode 4% begins to conduct current toward the gate of the silicon-controlled rectifier 40. The result is to close the circuit from the lamp 36 to negative bus 32 and thereby allow ilow or" current from the nickel-cadmium storage battery 26 through the transformer half-winding 22-20 and lamp 36 to negative bus 32. Lamp 36 thereupon lights.

When power is restored to transformer it the ambient lighting will also increase. When conventional illumination thus returns, the resistance of cadmium-sulfide resistor 44 decreases, thus reducing the flow of current to the gate of silicon-controlled rectifier 4h. The characteristics of a silicon-controlled rectifier are such that direct anode-cathode current would continue to fiow. Due to the half-cycle current characteristics of rectifier 4 3, however, this component will cease to conduct upon the first negative half-cycle of voltage supplied from transformer it). Once conduction has ceased, the rectifier will remain in the off position until a subsequent lighting failure occurs.

Secondary 18 of transformer it should have as low a resistance as possible so as to aitord negligible voltage drop between the battery 26 and lamp 345 during emergency operation. It must be so designed as to provide the minimal A.C. voltage override of the DC. battery voltage required to pass the silicon-controlled rectifier without damage to light 36. In an exemplary apparatus constructed in accordance with the invention, battery as is rated at 5.0 volts and 2.5 ampere-hours. Between terminal 22. and tap 2d there is a .25 ohm resistance and the no-load voltage of this section is 4.5 volts. Light 36 has a design voltage of 4.7 volts and a rated current of .590 ampere.

Capacitors 3S and Si) function to prevent the trigger ing of the silicon-controlled rectifier 4t? due to occasional transient conditions. Sir ilarly, resistor 52 provides sulficient bias voltage drop to keep the gate of the silicon-. controlled rectifier 4t? in the blocking state at high temperatures, even though no gate signal is present.

It will be understood that a number of variations may be made in the circuitry of this invention. For example, in the embodiment described above, capacitor 335 may be selected so as to pass sixty cycle current for normal lighting use providing a filter capacitor network is included to prevent the triggering of silicon-controlled rectifier 49 due to occasional transient conditions.

Another modification of this invention is shown in FIG. 2. The circuit of FIG. 2 functions in much the same manner as that of HG. 1. For this reason, similar elements in the two circuits are given similar numbers for ease of identification. The primary distinction between the circuits of FIG. 1 and FIG. 2 is that the siliconcontrolled rectifier it of the former is replaced by two rectifiers 54-, 5'6 in the latter. Silicon-controlled rectifier 54- receives its gating impulse from diode 43 in the same manner as silicon-controlled rectifier 4-0 of FIG. 1. However, in the embodiment of FIG. 2, the load current of the silicon-controlled rectifier 54 does not serve to light the lamp as, but rather serves to gate a second high current capacity silicon-controlled rectifier 55 by means of conductor Rectifier 54 is in parallel relationship with a capacitor as which serves to eliminate gating of rectifier 54 due to transient phenomena. Furthermore, this rectifier is in series with a resistor 62 and with a second rcsistor 64. The primary advantage of the circuit illustrated in PEG. 2 is that it makes it possible to switch heavier loads than can be handled by the circuit of FIG. 1.

FIG. 3 illustrates in pictorial form the construction of an emergency lighting unit according to the circuit diagram of FIG. 2. For ease of reference, circuit elements shown in FIG. 3 are given the same numbers as the corresponding elements shown in the schematic diagram of FIG. 2. In the illustrated embodiment, a sheet metal chassis 7d is provided with two cut-out portions 72 and 74. In cut-out 72 there is mounted a nickel-cadmium rechargeable storage battery 26 of a standard commercial make having output leads 7d, '78. In cutout portion 74 there is mounted an insulating panel 8h upon which are mounted a number of the circuit eiements. The lamp 3a is mounted in a socket 232 which in turn is supported by a copper bracket as which is L-shaped and rests on panel 8%. A hole 86 is provided in the side of the chassis and the photosensitive cadmium-sulfide resistor 44 is mounted at this position so as to be exposed to ambient light. A cover designated generally is so disposed as to be mounted over the chassis and its circuit elements. Cover 83 includes a metaliic side frame which is provided with a cutout opening 92. which fits around the exposed cadmium-sulfide photosensitive resistor 44. Ventilation holes 94 are also included to allow cooling of the internal elements. The upper side of frame 33 carries a translucent cover 96 which may be of glass or plastic. The entire frame 88 fits over the edge of chassis 7t) and may be secured by any suitable means, such as spring clips or screws which are not shown. It will be readily seen that the embodiment of FIG. 3 provides a compact, easily mounted luminaire of standard configuration for housing the elements of this invention.

Many other variations and modifications of this invention will be apparent to those skilled in the art. For this reason, the foregoing description is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An emergency lighting unit which comprises: transformer means having a primary winding connectable to an alternating current power source and a secondary winding including first and second terminals and a tap therebetween; rechargeable battery means having a first pole electrically connected to said first terminal and a second pole; voltage divider means electrically connected between said first and second poles; comprising a fixed resistor in electrical series relationship with a light sensitive resistor exposed to ambient light and having a voltage divider tap therebetween; solid state switching means having at least an anode, a cathode, and a gate, said gate being adapted to be energized from said voltage divider tap and said cathode being electrically connected to said second pole; light producing means electrically connected between said anode and the tap of said transformer means; and current rectifier means electrically connected between said second terminal and said second pole.

2. The apparatus of claim 2 wherein a gate current rectifier means is electrically connected between said voltage divider tap and said gate.

3. The apparatus of claim 3 wherein the gate circuit of a second solid state switching means is connected in series with said gate current rectifier means and said gate.

4. The apparatus of claim 4 wherein said emergency lighting unit is substantially completely contained in an enclosure unit and wherein at least a portion or said enclosure unit is adapted to transmit radiation from said light producing means therethrough.

5, The apparatus or" claim 3 wherein each of said current rectifier means and said gate current rectifier means is a solid state diode.

6. The apparatus of claim 6 wherein said switching means is a silicon-controlled rectifier.

7. The apparatus of claim 7 wherein said light sensitive resistor is a cadmium-sulfide resistor.

8. An electrical control circuit which comprises: transformer means having a primary Winding connectable to an alternating current source and a secondary winding; rechargeable battery means; rectifier means in series with said battery means to form a first series circuit; electrical conductor means connecting said first series circuit across at least a portion of said secondary winding; electrical load means; solid state switching means having an anode, a cathode, and a gate, the anode and cathode being connected in a second series circuit with said load means; conductor means connecting said second series circuit across said battery means and said secondary winding; and triggering circuit means connected to apply a positive voltage to said gate in response to a preselected stimulus to close the circuit through said switching means.

9. Environmental responsive means which comprises: transformer means having a primary winding connectable to an alternating current power source and a secondary winding including first and second terminals and a tap therebetween; rechargeable battery means having a first pole electrically connected to said first terminal and a second pole; voltage divider means electrically connected between said first and second poles, said voltage divider means including a voltage divider tap and being responsive to environmental changes to vary the voltage at said voltage divider tap; solid state switching means having at least an anode, a cathode, and a gate, said gate being electrically connected to said voltage divider tap and said cathode being electrically connected to said second pole; utilization means electrically connected in series with said anode and the tap of said transformer means; and current rectifier means electrically connected between said second terminal and said second pole.

References Cited in the file of this patent UNITED STATES PATENTS 2,995,695 Reich Aug. 8, 1961 OTHER REFERENCES Tung-Sol Tips, No. 16, February 1961, Tung-Sol Electric Inc. (Figure 9 relied on).

UNITED STATES PATENT OFFICE Patent N06 3,159,755

It is hereby certified that error appears in the above numbered pat- CERTIFICATE OF CORRECTION- December 1 196 .1

ent requiring correction and that the said Letters Patent should read as corrected below.

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numeral "7" (SEAL) Attest:

for the claim reference numeral "2" reference numeral "3" reference numeral "4" reference numeral "3" reference numeral "6" for the claim reference Signed and sealed this 20th day of April L965 ERNEST W. SWIDER Aitesting Officer EDWARD J. BRENNER Commissioner of Patents Patent N06 UNITED STATES: PATENT OFF IQE CERTIFICATE OF CORRECTION- December 1 19641 T. Dance-n It is hereby certified that error appears in the above numbered patent requiring correction and that the 'said Letters Patent should read as corrected below.

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Column 5,

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for the claim reference Signed and sealed this 20th day of April l 965 ERNESTJW. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. AN EMERGENCY LIGHTING UNIT WHICH COMPRISES: TRANSFORMER MEANS HAVING A PRIMARY WINDING CONNECTABLE TO AN ALTERNATING CURRENT POWER SOURCE AND A SECONDARY WINDING INCLUDING FIRST AND SECOND TERMINALS AND A TAP THEREBETWEEN; RECHARGEABLE BATTERY MEANS HAVING A FIRST POLE ELECTRICALLY CONNECTED TO SAID FIRST TERMINAL AND A SECOND POLE; VOLTAGE DIVIDER MEANS ELECTRICALLY CONNECTED BETWEEN SAID FIRST AND SECOND POLES, COMPRISING A FIXED RESISTOR IN ELECTRICAL SERIES RELATIONSHIP WITH A LIGHT SENSITIVE RESISTOR EXPOSED TO AMBIENT LIGHT AND HAVING A VOLTAGE DIVIDER TAP THEREBETWEEN; SOLID STATE SWITCHING MEANS HAVING AT LEAST AN ANODE, A CATHODE, AND A GATE, SAID GATE BEING ADAPTED TO BE ENERGIZED FROM SAID VOLTAGE DIVIDER TAP AND SAID CATHODE BEING ELECTRICALLY CONNECTED TO SAID SECOND POLE; LIGHT PRODUCING MEANS ELECTRICALLY CONNECTED 